That's pretty heavy! My guess is you may need extra leafs at the rear along with your new shocks. Your best bet is to contact Agile Offroad for their heaviest valved Fox shocks. If your near their shop they'll be able to do custom leafs for you but if not they should be able to send you an extra leaf.
I just went through this. Mine is 5800lbs at the rear (Ambo) and already comes with 9 or 10 leafs. Agile added 2 leafs and re-arch my leafs pack along with their Fox shocks, world of difference!
Sent from my SGP511 using Tapatalk
2008 E350 Hambo
2001 E350 AmbuLand (sold)
1970 Econoline popup camper
1965 Econoline Travelwagon
A few bicycles...and sandals ;)